The invention discloses a sewage treatment system which comprises a heavy sedimentation lattice, a fiber sedimentation lattice and an overflowing lattice. The heavy sedimentation lattice and the fiber sedimentation lattice share a first partition wall. The fiber sedimentation lattice and the overflowing lattice share a second partition wall. The overflowing lattice is a right angle trapezoid in the longitudinal cross section. The bottom face of the trapezoid is connected with the second partition wall. The top face of the overflowing lattice is perpendicular to the second partition wall. The first partition wall and the second partition wall are provided with hole openings correspondingly. The hole opening in the second partition wall is lower than the hole opening in the first partition wall. The wall of the heavy sedimentation lattice is provided with a plain boiled water inlet. The wall of the overflowing lattice is provided with an overflowing opening communicating with a biochemical treating pond. According to the system, by arranging the heavy sedimentation lattice, the fiber sedimentation lattice and the overflowing lattice and forming the openings in the partition walls, useful substances in plain boiled water can be separated out and recycled, resources can be saved greatly, and the groundwork is laid for follow-up sewage treating working procedures.